document.addEventListener('visibilitychange', function() {
    console.log("x")
    var isHidden = document.hidden;
    var icon=document.getElementsByTagName("link");
    if (isHidden) {
        document.title = "倪:'你快回来'";
        icon[0].href="images/l.png";
        console.log("y")

    } else {
        document.title = "谢:'我回来啦'";
        icon[0].href="images/h.png"
        console.log("z")
    }
});